This invention relates to a process for preserving the natural red color of freshly butchered meat and to an interleaf for placement between layers or slices of freshly butchered meat to preserve the natural red color thereof.
The modern consumer associates a bright red color of meats, such as beef, pork, lamb and veal, with freshness. It is well known that these meats rapidly lose their bright red color after butchering and turn a brownish color under certain conditions.
This brown coloration is due primarily to chemical changes of the pigment myoglobin present in the meat. In its reduced form, myoglobin imparts a purple-red color to the meat. Oxymyoglobin, which is bright red, and metmyoglobin, which is a grayish-brown color, are both obtainable from reduced myoglobin. Upon being exposed to air after the meat is cut or ground, myoglobin takes up oxygen from the air and is converted by an oxygenation process to oxymyoglobin. On the other hand, exclusion of air from the surface of the fresh cut or ground meat hastens the production of metmyoglobin with a resultant discoloration which is undesirable from the consumer's point of view. The chemistry responsible for these color changes with respect to the availability of oxygen has been well investigated by various researchers and is summarized in an article entitled, "The Chemistry of Meat Pigments", Journal of Agricultural Food Chemistry, Vol. 14, pp. 207-10 (May-June, 1966).
When slices of freshly cut meat, such as beef steaks, are stacked on top of each other during butchering, air necessarily is excluded from the adjoining surfaces and these surfaces turn a brownish color within a few hours. To alleviate this problem, it has been common practice to place sheets of porous paper between the individual slices of meat. The trace amounts of air trapped in the fibrous structure of such a paper interleaf apparently is sufficient to delay the formation of the undesired metmyoglobin and other discoloring pigments. The desired red color can be prolonged further by impregnating the paper with certain additives which inhibit the formation of metmyoglobin and other discoloring pigments.
Such a paper interleaf tends to absorb moisture from the meat and is highly susceptible to tearing and/or sticking on the meat while being removed prior to packaging of the meat. The added time required to remove all of the fragments of the paper interleaf from the meat reduces the efficiency of the packaging process. Sheets of synthetic plastic films, such as polyethylene and polypropylene, should be better suited for this purpose because these materials are not weakened by wetting and otherwise have a higher strength. However, it has been found that, when conventional plastic films are used as a meat interleaf, they do not inhibit discoloration of the meat. Instead, the meat turns a brownish color in about the same time asif no interleaf were used.
One approach commonly employed for preserving the red color of fresh meat is to provide an oxygen permeable film for packaging the meat which permits sufficient oxygen from the atmosphere to diffuse therethrough and contact the meat to maintain myoglobin in an oxygenated state. Representative of such packaging material is disclosed in U.S. Pat. Nos. 2,676,943 (Carson), 2,835,595 (Salatiello), 2,900,260 (Snyder et al), 2,931,732 (Hoffman et al), 3,003,884 (Andrews) and 3,423,212 (Purcell et al). These packaging films generally are not suitable for use in an interleaf. The stacked meat effectively excludes the entry of atmospheric air which is necessary for replenishing the oxygen required to maintain the myoglobin in an oxygenated state. While such films are oxygen permeable, they typically do not have the degree of porosity required to trap a sufficient amount of available oxygen to prevent the undesired discoloration of the meat within a relatively short period of time.
Another approach commonly employed for preserving the red color of fresh meat is to treat the meat with various chemicals which, through a chemical mechanism not fully understood, inhibit the formation of metmyoglobin and other discoloring pigments. These chemicals typically are applied to the meat prior to packaging. For example, U.S. Pat. No. 2,863,777 (Dekker) discloses that the red color of fresh meat can be preserved for at least 12 hours by sprinkling, spraying, or injecting the meat with a mixture of beta-substituted pyridine and ascorbic acid prior to packaging. U.S. Pat. Nos. 2,491,646 (Coleman) and 3,600,200 (Bernholdt et al) disclose a similar treatment with nicotinic acid. U.S. Pat. Nos. 3,266,909 (Ellis), 3,615,691 (Duiven et al), 3,821,437 (Heller et al) and 3,867,558 (Sato et al) respectively disclose the use of glutamic acid salts, tetrazoles, beta-carotene and hydroxypyrones for this purpose.
Such conventional color preservatives cannot be incorporated into a thermoplastic polymeric film because they tend to decompose at temperatures below those normally used for forming such films.